The present invention relates generally to optical switches and more particularly to optical switches having a plurality of movable mirrors.
There has been considerable interest in switches for switching light from one optical fiber to another or from a free space optical beam to one or more optical fibers, particularly for telecommunications and digital data networking. A variety of switch configurations are of interest, including 1xc3x972, 1xc3x97n, and nxc3x97n, where n is a number from 2 to about 64. A variety of principles have been utilized in prior art switches, including electro-optical effects and electromechanical actuators, and working switches are now commercially available using these techniques. The prior art switches are very expensive and rather large.
Prior art 1xc3x97n electromechanical optical fiber switches have typically either moved the input fiber so that it is in communication with the desired output fiber, moved a single mirror so that the input light couples to the desired output fiber or moved a refractive optical element until the desired coupling is obtained. Typically collimating lenses are arranged at each optical fiber so that a collimated beam is being switched by the electromechanical actuator. An example of such a switch is described in U.S. Pat. No. 4,322,126 by Minowa et. al., where a prism-like structure is moved between input and output optical fibers. An alternative prior art approach where a single mirror is translated to deflect a collimated beam into multiple output fibers is described in U.S. Pat. No. 5,208,880 by Riza et. al. Various approaches have used a single rotating mirror to couple light into a plurality of output fibers, such as described in U.S. Pat. No. 5,647,030.
Most of the prior art approaches have used a single electromechanical actuator, either a linear or angular actuator, to deflect the input optical beam because the prior art electromechanical actuators have been large and expensive. The single electromechanical actuator has typically had a mechanism to accurately control the position of the mirror in order to accurately couple the light into the output fiber. This accurate mirror positioning also increases the size and cost of prior art actuators, particularly for numbers of output fibers larger than two, where simple methods are not readily available for achieving the required position resolution.
Most of the prior art optical switches are designed for use in telecommunications application where the wavelength of light used is typically 1.5 microns or 1.3 microns in the infrared. Also many of the prior art switches have been designed for use with a so-called multi-mode optical fiber, which has a relatively large central core that carries the light, especially for use in the infrared. The positional accuracy necessary for achieving high optical coupling is on the order of one fifth the diameter of the central optical core of the optical fiber. Most multimode fiber for use in the infrared has a core diameter of about 50 microns, so that positional accuracy in coupling need only be to within about 10 microns, which can be achieved using conventional techniques.
It is desirable in many optical systems to use a so-called single-mode optical fiber that can achieve greater optical bandwidth. The core diameter of these fibers is about eight microns for use in the infrared and about four microns for use with red light. The required positional accuracy is thus reduced to less than 1 micron for these systems, about a factor of ten less than for prior art multimode optical switches.
Microstructures fabricated using silicon integrated circuit processing techniques have been developed for a variety of sensing and actuation applications. Compared to conventional prior art implementations in these and other applications, micro-structures provide advantages in cost, reliability and performance. Integrated actuators, that is, microstructures where the actuator is fabricated simultaneously with the mechanical structure, are advantageous from the standpoint of cost, reliability and ease in assembly.
Various actuation methods have been used for integrated actuators for microstructures including electrostatic, electromagnetic, thermal and thermo-pneumatic. The thermal techniques tend to provide large force but with relatively slow response times. Electromagnetic techniques are complicated by the difficulty in providing integrated coils with sufficient number of turns in a planar structure and the high power dissipation caused by the high currents needed to produce the desired magnetic field. Electrostatic actuation becomes attractive on a small size scale as the forces increase as the gap between elements decrease. The power dissipated by electrostatic elements tends to be low and the operating speed is usually limited only by the mechanical response of the structure.
The driving forces in prior art electrostatic actuators have been typically created using only one of two types of driving electrodes: so-called comb drive fingers or parallel plates. Parallel plate capacitors generate a force that is proportional to the square of the drive voltage and inversely proportional to the square of the gap between the plates. For practical microstructure elements, the useful range of motion for parallel plate actuators is less than 10 microns. Comb drive actuators, such as described in U.S. Pat. No. 5,025,346 to Tang et al., feature a series of interdigitated electrodes whose capacitance may be used to provide a motive force that is relatively constant over a range of motion roughly equal to the length of the comb fingers, which can be made greater than 100 microns. The force available from each finger is relatively small, so that practical comb drive actuators typically have between 10 and 200 fingers to produce adequate force for a microstructure device.
The early comb drive actuators used thin, polysilicon layers provided by the so-called surface micro-machining process to fabricate the comb fingers and the moveable, laterally-driven element. This polysilicon was typically 1-2 microns thick. Since the lateral feature size of these devices was comparable to the material thickness, the stiffness of the parts to out-of-plane deflections was very low. The advent of Deep Reactive Ion Etching (DRIE) has allowed similar structures to be fabricated in single crystal silicon with typical thicknesses of 100 microns. DRIE is described in a paper entitled, xe2x80x9cSilicon Fusion Bonding And Deep Reactive Ion Etching; A New Technology For Microstructuresxe2x80x9d By Klassen, Petersen, Noworolski, Logan, Maluf, Brown, Storment, McCully, and Kovacs, in the Proceedings Of Transducers ""95 (1995), pages 556-559. These thicker structures can provide larger vertical electrode areas and substantially higher stiffnesses out of the plane of deflection. Recently, other fabrication techniques, including thicker surface micro-machined polysilicon or plated metal structures made in photolithographically defined molds have been used to increase the thickness and thus the out-of-plane stiffness of comb drive structures.
In general, it is an object of the present invention to provide an optical microswitch which overcomes the foregoing disadvantages.
Another object of the invention is to provide an optical microswitch of the above character which utilizes at least one electrostatic microactuator having at least one comb drive assembly therein.
Another object of the invention is to provide an optical microswitch of the above character in which a plurality of electrostatic microactuators are aligned along at least one hall of the microswitch.
Another object of the invention is to provide an optical microswitch of the above character for use in a magneto-optical data storage system.
The present invention provides optical switches and the like utilizing large deflection high speed microactuators. The microactuators may be used in optical switches of a variety of designs. The optical switch may be used in a variety of systems such as magneto-optical data storage systems, telecommunications systems or data transmission systems.